He's hardly abusive...
Things hurt in relationships. A lot. People say things/don't say things, do things/don't do things which can sting badly, but it doesn't mean they intended to hurt the other.
Seb has hurt Len before, Len has hurt Seb before.
This is in no way the last or the biggest problem they will face, but it's been tackled, and I think the best way everyone could help now is by letting this lie and not churning it up again, even with the best of intentions.